Increasing the output speed of rotary printing machines is sometimes limited by the output apparatus to which the machines are coupled. One such output apparatus is a longitudinal folding apparatus. Longitudinal folding apparatus usually are so constructed that the material to be folded is passed transversely with respect to its supply direction through folding rollers. It is important that the rear or trailing edge of the product to be folded, during the folding operation, which no longer moves in the supply direction, has left the plane of the next product to be folded before the next product to be folded arrives. The time which is required for the product which is being folded until its trailing edge leaves the plane of the supply or transport belts--which are usually provided--is considerable and, upon high-speed production, the transport system may pass over a substantial distance. During that time, and as this distance is passed, a subsequent printed product may be supplied. The subsequent printing product, however, must be prevented from engaging or impinging on the product which is just being folded since, otherwise, the products may be damaged, or shifted in position, that is, the product then being folded may no longer be folded along the predetermined folding line.
It has previously been proposed--see the referenced German Patent Publication DE-AS No. 1 204 689--to split the stream of the products to be folded to two paths, each one being directed to an individual longitudinal folding apparatus. This solution, while providing for high-speed output, is expensive since it requires duplication of the folding apparatus, additional space for the additional folding apparatus, and for the additional transport path.